runtime(erlang): Add support for triple-quoted strings and docstrings

runtime(erlang): Add support for triple-quoted strings and docstrings

Erlang recently added the `-moduledoc` attribute as well as triple
quoted strings and the `~` prefix for binary strings, see [1].

Erlang also added nominal types. See EEP-69 [2].

This commit removes the documentation of "g:erlang_highlight_bifs" and
"g:erlang_highlight_special_atoms", which are not longer supported.
"g:erlang_old_style_highlight" is kept undocumented (as it should not be
used by new users).

This commit contains the modifications in the following PR and commits:

- vim-erlang/vim-erlang-runtime#58
- vim-erlang/vim-erlang-runtime@43d18d3
- vim-erlang/vim-erlang-runtime@ac88ebf
- vim-erlang/vim-erlang-runtime@19c1be9
- vim-erlang/vim-erlang-runtime@7f5cefc
- vim-erlang/vim-erlang-runtime@976b10b

[1]: https://www.erlang.org/doc/system/documentation.html
[2]: https://www.erlang.org/eeps/eep-0069

closes: #17687

Co-authored-by: Johannes Christ <jc@jchri.st>
Signed-off-by: Csaba Hoch <csaba@cursorinsight.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>